The system was first put into operation in 1951. It’s function is both familiar and foreign. First off, it uses decimal rather than binary for its calculations. And instead of transistors it uses electromechanical switches like are found in older automatic telephone exchanges. This makes for very noisy and slow operation. User input is taken from strips of paper with holes punched in them. As data is accumulated it is shown in the registers using decatrons (which have since become popular in hobby projects). Luckily we can get a look at this in the BBC story about the WITCH.

According to the eLinux page on the device, it was disassembled and put into storage from 1997 until 2009. At that point it was loaned to the museum and has been undergoing cleaning, reassembly, and repair ever since.

There’s a paper from 1951 linked from the eLinux page. The Computer Conservation Society website has some interesting material, including a programming manual:http://www.computerconservationsociety.org/witch.htm . This machine was once used to teach computing, after all.

The memory stores on this computer use Dekatron glow transfer counting tubes to store each digit. There are two types used, the GC10B (the ones that glow orange), which are common, and the GC10A (the ones that glow purple), which are frightfully rare. Back when the team first started to restore this device, they caused a stir in the tube collector community by putting out a request looking for a donation of 800 or so GC10A tubes, wholly unaware that most tube collectors assumed there were less than 800 GC10A tubes left in the entire world, period. Fortunately the GC10A and GC10B are largely interchangeable; I strongly suspect they are keeping most of the ample stock of GC10A’s they found with the computer in storage and using much more common GC10Bs wherever possible.

Seeing things like this always makes me appreciate the amazing technology we have sitting at our fingertips :) (Oh, and I really want to take a laptop back in time, you know, just to screw with them a bit!)